1. Field of the Invention
The present invention relates to an improved lower end for a positive pulse measurement while drilling (MWD) tool. Specifically, the improved lower end has the ability to prevent or reduce the entry of lost circulation material (LCM) and debris into the lower end through standard mud port holes. Reducing the entry of LCM and debris, especially larger sized LCM and debris, helps prevent the signal shaft from clogging or becoming inoperable.
2. Description of the Related Art
Positive pulse MWD tools are commonly used in the oil and gas industry as an effective means for determining the real-time location of the drill bit for purposes of making adjustments to drilling strategies. The standard positive pulse MWD system is comprised of multiple tubular housings comprising of at least a helix housing, poppet housing, pulser, directional module, and battery housing, among others.
The traditional positive pulse MWD system relies on a signal shaft or piston to interrupt the flow of drilling mud within the drilling string. This interruption of the drilling mud flow results in a positive pulse that machinery outside the well interprets to determine the location of the drill. An example of a typical MWD system is described in U.S. Pat. No. 5,333,686. The standard poppet housing is a tube with a substantially uniform outer diameter throughout the length of the poppet housing with a series of fluid ports located near the downwell end.
Traditional positive pulse MWD lower ends suffer from repeated clogging from debris or lost circulation material (LCM) entering the fluid ports located on the poppet housing of the lower end. During normal drilling operations, drilling mud is lost into the formation due to cracks in the rock or other geographic features. When enough drilling mud is lost to affect operations, drillers pump LCM down the drill string in an effort to seal up the cracks within the formation. LCM is comprised of numerous different types of material such as pieces of cotton seed hulls, walnut shells, seeds, bark, etc. that have sufficient volume and mass capable of filling the cracks in the formation that result in loss of drilling mud. Other debris also may present in drilling mud from cuttings not properly filtered as drilling mud is recycled.
Standard positive pulse MWD tools may become clogged and ineffective due to LCM or other debris entering the drilling fluid port(s). When this occurs, the signal shaft ceases to operate properly and the entire drill string must be removed so the lower end and signal shaft can be cleared of debris. Depending on the depth of the drill string, this clogging may result in a 12 to 24 hour delay, costing tens of thousands of dollars, while the signal shaft is cleared of debris. A secondary result of the common clogging of the lower end is that drillers tend to utilize less LCM which reduces the effectiveness of preventing the loss of drilling mud. As a result, many operators reduce LCM flow rates from the standard of 40 to 50 pounds per barrel to 15 pounds per barrel.